Hope this helps...... 351 Engine Swap - 5.0 Mustang & Super Fords Magazine
The 351W is a Windsor class engine. It is made on the same factory line as our beloved 5.0. However, the 351 posseses several qualities that make it a desirable block for an engine buildup. The advantages of using a 351W vs a 5.0 (302):
Obviously, you get an extra 49 cubic inches of displacement. As the saying goes, there is no replacement for displacement. Second, the webbing in the lower half of the block is thicker, making the block stronger. Third, the crank has bigger main and rods journals, making the cranks more durable than their 302 counterparts.
FACTS: What you need to know/consider when you swap a 351W into a Fox3 platform chassis:
The 351 block is very similar to the 302. That means that almost all parts swap between a 302 and a 351. This includes: Heads, cam, lifters, timing chain, timing chain cover, water pump, engine mounts, and all sorts of other stuff. The bellhousing bolt pattern is the same as a 302, so all trannies that bolt to a 302 will bolt to a 351. However, there are some differences in the 351 that necessitate new parts:
1) The oil pan is different. Motorsports carries one. You can also get an oil pan of of an early eighties LTD Crown Vic. If you go the junkyard route, remember you also need a oil pan pickup tube, and a special main bolt that the pickup attaches to. The FMS pan is a pretty good deal, and if you shop around, you can get one for under $100, which comes with the dipstick, bolt, and pickup tube.
2) The internal balance of a 351W is the same as pre-81 302's (28.2 oz). The 5.0 HO has a 50 oz. unbalance, which means you cannot use the flexplate/flywheel or the harmanic balancer off of an HO engine. You have to get the correct pieces from a dealer/junkyard.
3) The deck height is higher, which means you need a different intake, since the 351W intake is wider. A 5.0 Upper will bolt to a 351W lower.
4) Also, a higher deck height means that the accessory bracket will need to be replaced. FMS sells the new bracket for about $50.
5) The higher deck height means the headers sit up higher than in a 302 powered Mustang. A special set is required for a 351.
6) A 351W will in all likelyhood not clear the stock hood. You will need a cowl hood for your car.
7) The distributor has a fatter shaft. You can obtain one from a 351W powered FI truck (if you are using FI) or any late 70's/early 80's car using the 351W and a Duraspark system if you are going to build a non-efi car.
Those are the major differences. As you can see, for about $1000 you can put a 351W in your Mustang. This is cheaper than a stroker, plus you wind up with a more reliable engine.
Tips: There are several things to look out for to ensure that your swap to a 351W is easier and more successful. They are as follows:
1) A high volume oil pump
WILL NOT clear the FMS pan. If you want to run an HV pump, you must either modify the pan or buy a Canton or similar pan, for many dollars more. The modifications just include cutting down the front drain bolt, and welding on a corner to the pan to clear the pump housing.
2) Get new motor mounts. If your mounts are questionable already, the additional weight of the 351W will make them fail in a hurry. I recommend the 87-93 convertable mounts, which will work in any 79-93 Mustang.
more swap info.....
351w Swap Info.
Will it fit?
The deck height of a 351w is 9.480" for 1969-1970 blocks and 9.503" for 1971 and up blocks compared to the 8.2" deck height of the 302w block. This equates to a taller and wider motor. There have been many people who have squeezed 351's under the stock Mustang hood, but chances are at least a 1.5" cowl hood will be needed for the 351w combination. The motor mounts on 351w and 302w blocks are interchangeable. Can I reuse any 302w parts on the 351w?
There are many interchangeable parts between the Windsor blocks. The 351w uses a wider intake than the 302w, but you can use a cobra upper with a 351w specific lower intake. Timing covers, water pumps, and several of the accessory brackets are interchangeable. You do need a FMS power steering and a/c bracket in most cases. Cylinder heads from a 302 can be used on a 351w block by drilling the head boltholes to accommodate the larger 1/2" 351w head bolts. The 302w fuel rail can be modified to fit the 351w by extending the rail crossover tube. Will my 302w balancer work on my 351w?
The 351w uses a 28oz/in imbalance that is the same as early 302's. You can use a 28oz/in 302 balancer on the 351w. What is needed to use the serpentine belt setup from a 302 on a 351w?
The 302 alternator bracket can be utilized on the 351w, along with the reverse rotation water pump along with the air conditioning and power steering brackets. The crank pulley requires a 3/8" spacer available from FRPP between it and the balancer for proper pulley alignment. What do I need for exhaust on the 351w?
Swap headers are a must for a proper 351w installation. There are many suppliers of 351w swap headers and matching intermediate pipes including: Hooker Headers, Hedman, BBK, Mac, and Kooks. Most 351's will benefit from a 1 3/4" primary tube size. What parts are a must have for a 351w installation?
First, you need an oil pan and matching pickup to mount the 351w into the Mustang that will clear the K-member. Moroso, Miloden, Canton, and FRPP all make exceptional 351w Mustang swap oil pans. Note that the FRPP version is a 5-quart capacity design while the others are 7 quarts. Crown Vicorias and Grand Marquis also have a dual sump 5-quart oil pan that will fit the Mustang K-member. Second, an intake is needed. If you are using EFI Edelbrock and TFS make intakes for EFI equipped 351's. You can also use a FRPP Cobra upper with a matching lower, or a 351w truck lower with stock EFI Mustang upper. For carbureted applications there are many companies making 351w carburetor intakes such as: Edelbrock, Holley, Weiand, and Offenhouser. You will need a 351w specific distributor. MSD and EFI equipped 351w Thick Film Ignition distributors will work with the Ford EFI EEC. Any points, Duraspark, or MSD distributor will work with a carbureted combination. What block should I use?
All pre 1994 factory 351w blocks are non-roller designs. Blocks produced before the early 1980's used a two-piece rear main seal. Ford trucks and vans produced after the mid 70's use a stronger rod design often referred to as 'Football' rods because of their football shaped bolt heads. 1969-1970 blocks had a lower deck height (9.480") and provide more compression from the factory. These early blocks also have a stronger thick wall casting design and are often thought of as the strongest factory 351w block. Keep in mind that all 351w blocks are considerable stronger than the factory 302w block. If you need an exceptionably strong 351w block design FRPP and Dart both offer aftermarket 351w blocks in many varieties. How do I install a roller cam in my 351w?
The easiest way to use a roller cam in the 351w is to find a F4TE casting number block from 1994 and later F-series trucks and E-series vans. If you happen to have a block produced before 1994 you can retrofit a roller cam quite easily. The first option is using 5.0L hydraulic roller lifters, retention spider, and lifter link bars with a reduced base circle hydraulic roller camshaft. This method requires machining the lifter valley to accept the spider bolts. Second, Comp, Crane, and Crower make retrofit roller lifter that will allow the use of any off the shelf 5.0L style hydraulic roller cam to be used in a non-roller 351w block. Any flat tappet 351w-302w flat tappet camshafts will work with the correct corresponding firing order. What vehicles should I get my 351w from at a junkyard?
Ford produced many vehicles which used 351w motors including, but not limited to, the following... Mustangs Fairlanes Galaxies Cyclones Torinos LTD's Crown Victorias Grand Marquis Rancheros Cougars F-series trucks E-series vans Broncos What about a fuel system?
The 351w is defiantly going to consume fuel at a higher rate than a smaller motor and you should upgrade the stock fuel system to provide for this thirst. EFI equipped Mustangs should use at least a 190lph in tank fuel pump and 24+ pound injectors. Many carbureted Mustangs use a Holley Blue pump or equivalent, which requires slight modifications to the stock in tank fuel pick-up to function properly. An adjustable fuel pressure regulator should be utilized with both EFI and carbed systems. 
351 to F0X SWAP 
